Anesthetic depth measuring apparatus

ABSTRACT

From a fluctuation of pulse periods of a subject continuously measured by a pulse period measuring device, a first pulse period fluctuation signal HFC RR  which corresponds to a first pulse period fluctuation component produced in substantial synchronism with a respiration of the subject and a second pulse period fluctuation signal LFC RR  which corresponds to a second pulse period fluctuation component having a predetermined frequency lower than a frequency of the first pulse period fluctuation component are extracted by a pulse period fluctuation signal extracting means. Then, based on a ratio (HFC RR  /LFC RR ) of the first pulse period fluctuation signal HFC RR  to the second pulse period fluctuation signal LFC RR , an anesthetic depth of the subject is calculated by an anesthetic depth calculating means. Thus, the present apparatus can objectively or quantitatively calculate the anesthetic depth of the subject. Additionally, the apparatus can accurately measure the anesthetic depth of the subject without needing operator&#39;s skill or the like.

FIELD OF THE ART

The present invention relates to an anesthetic depth measuring apparatusfor measuring an anesthetic depth of a living subject.

BACKGROUND OF THE INVENTION

When a patient is anesthetized for a surgery or the like, it is requiredto maintain a suitable anesthetic depth so as to protect the patientfrom stress or pain due to the surgery. Conventionally, for example, ananesthetic depth has been subjectively or empirically recognized bymonitoring a change of a blood pressure, a heart rate or a respirationrate of the patient, resulting from a stimulation of the surgery, orobserving a reflex of eyelashes, a dimension of a pupil, a hue of a limbor a body temperature of the patient.

However, since the anesthetic depth recognition based on the change ofthe blood pressure, the heart rate or the respiration rate, or based onthe reflex of the eyelashes, the dimension of the pupil, the hue of thelimb or the body temperature is performed depending on a subjectivejudgement of anesthetists or the like, the anesthetists are required tohave a long-time experience and a skill. In addition, it is not easy toobjectively or accurately recognize the anesthetic depth. It istherefore an object of the present invention to provide an anestheticdepth measuring apparatus for objectively measuring an anesthetic depthof a living subject.

The inventors of the present invention have continued their study in thebackground of the above described situation, and they have found that amagnitude of a pulse period fluctuation component produced insynchronism with a respiration of a subject, a magnitude of a bloodpressure fluctuation component having a frequency lower than a frequencyof the respiration of the subject or a rate of change of the pulseperiod to the blood pressure of the subject has a close relation to anactivity level of subject's parasympathetic nerve or sympathetic nerve,whereby an anesthetic depth of the subject can be objectively measuredon the basis of the magnitude of the above mentioned fluctuationcomponent, when the subject is anesthetized.

Moreover, the present inventors have found that the influences of theanesthesia on a peripheral body temperature and a deep body temperatureare different from each other, and a difference between the peripheralbody temperature and the deep body temperature has a close relation toan activity level of a nerve of the subject, whereby an anesthetic depthof the subject can be objectively measured on the basis of thedifference. The present invention has been developed based on thosefindings.

DISCLOSURE OF THE INVENTION

The above object may be achieved according to the first invention whichprovides an anesthetic depth measuring apparatus for measuring ananesthetic depth of a living subject, characterized by comprising: (a) apulse period measuring device which continuously measures a period of apulse of the subject; (b) pulse period fluctuation signal extractingmeans for extracting, from a fluctuation of the pulse periodscontinuously measured by the pulse period measuring device, a firstpulse period fluctuation signal which corresponds to a first pulseperiod fluctuation component produced in substantial synchronism with arespiration of the subject and a second pulse period fluctuation signalwhich corresponds to a second pulse period fluctuation component havinga predetermined frequency lower than a frequency of the first pulseperiod fluctuation component; and (c) anesthetic depth calculating meansfor calculating an anesthetic depth of the subject based on a ratio ofthe first pulse period fluctuation signal to the second pulse periodfluctuation signal.

In the above mentioned apparatus, from a fluctuation of the pulseperiods continuously measured by the pulse period measuring device, thefirst pulse period fluctuation signal which corresponds to the firstpulse period fluctuation component produced in substantial synchronismwith the respiration of the subject and the second pulse periodfluctuation signal which corresponds to the second pulse periodfluctuation component having a predetermined frequency lower than afrequency of the first pulse period fluctuation component are extractedby the pulse period fluctuation signal extracting means. Then, based ona ratio of the first pulse period fluctuation signal to the second pulseperiod fluctuation signal, the anesthetic depth of the subject iscalculated by the anesthetic depth calculating means. Thus, the presentapparatus can objectively or quantitatively calculate the anestheticdepth of the subject. Additionally, the apparatus can accurately measurethe anesthetic depth without needing operator's skill or the like.

The above object may be achieved according to the second invention whichprovides an anesthetic depth measuring apparatus for measuring ananesthetic depth of a living subject, characterized by comprising: (a) ablood pressure measuring device which continuously measures a bloodpressure value of the subject; (b) blood pressure fluctuation signalextracting means for extracting, from a fluctuation of the bloodpressure values continuously measured by the blood pressure measuringdevice, a blood pressure fluctuation signal which corresponds to a bloodpressure fluctuation component having a predetermined frequency lowerthan a frequency of a respiration of the subject; and (c) anestheticdepth calculating means for calculating an anesthetic depth of thesubject based on a magnitude of the blood pressure fluctuation signal.

In the above mentioned apparatus, the blood pressure value of thesubject is continuously measured by the blood pressure measuring device,and, from a fluctuation of the continuously measured blood pressurevalues, the blood pressure fluctuation signal which corresponds to theblood pressure fluctuation component having a predetermined frequencylower than a frequency of the respiration of the subject is extracted bythe blood pressure fluctuation signal extracting means. Then, based on amagnitude of the blood pressure fluctuation signal, the anesthetic depthof the subject is calculated by the anesthetic depth calculating means.Thus, the present apparatus can objectively or quantitatively calculatethe anesthetic depth of the subject. Additionally, the apparatus canaccurately measure the anesthetic depth without needing operator's skillor the like.

The above object may be achieved according to the third invention whichprovides an anesthetic depth measuring apparatus for measuring ananesthetic depth of a living subject, characterized by comprising: (a) apulse period measuring device which continuously measures a period of apulse of the subject; (b) a blood pressure measuring device whichcontinuously measures a blood pressure value of the subject; (c) changerate calculating means for calculating a rate of change of one of theblood pressure values continuously measured by the blood pressuremeasuring device and the pulse periods continuously measured by thepulse period measuring device, to the other of the blood pressure valuesand the pulse periods; and (d) anesthetic depth determining means fordetermining an anesthetic depth of the subject based on the rate ofchange calculated by the change rate calculating means.

In the above mentioned apparatus, the pulse period of the subject iscontinuously measured by the pulse period measuring device, the bloodpressure value of the subject is continuously measured by the bloodpressure measuring device, and a rate of change of one of the bloodpressure values and the pulse periods to the other of the blood pressurevalues and the pulse periods is calculated by the change ratecalculating means. Then, based on the rate of change, the anestheticdepth of the subject is determined by the anesthetic depth determiningmeans. Thus, the present apparatus can objectively or quantitativelydetermine the anesthetic depth of the subject. Additionally, theapparatus can accurately measure the anesthetic depth without needingoperator's skill or the like.

The above object may be achieved according to the fourth invention whichprovides an anesthetic depth measuring apparatus for measuring ananesthetic depth of a living subject, characterized by comprising: (a) aperipheral body temperature measuring device which measures a peripheralbody temperature of the subject; (b) a deep body temperature measuringdevice which measures a deep body temperature of the subject; (c)temperature difference calculating means for calculating a differencebetween the peripheral body temperature measured by the peripheral bodytemperature measuring device and the deep body temperature measured bythe deep body temperature measuring device; and (d) anesthetic depthdetermining means for determining an anesthetic depth of the subjectbased on the difference calculated by the temperature differencecalculating means.

In the above mentioned apparatus, the difference between the peripheralbody temperature measured by the peripheral body temperature measuringdevice and the deep body temperature measured by the deep bodytemperature measuring device is calculated by the temperature differencecalculating means. Then, based on the difference calculated by thetemperature difference calculating means, the anesthetic depth of thesubject is determined by the anesthetic depth determining means. Thus,the present apparatus can objectively or quantitatively determine theanesthetic depth of the subject. Additionally, the apparatus canaccurately calculate the anesthetic depth without needing operator'sskill or the like.

The above object may be achieved according to the fifth invention whichprovides an anesthetic depth measuring apparatus for measuring ananesthetic depth of a living subject, characterized by comprising: (a) aperipheral body temperature measuring device which measures a peripheralbody temperature of the subject; (b) a deep body temperature measuringdevice which measures a deep body temperature of the subject; (c)temperature ratio calculating means for calculating a ratio of theperipheral body temperature measured by the peripheral body temperaturemeasuring device to the deep body temperature measured by the deep bodytemperature measuring device; and (d) anesthetic depth determining meansfor determining an anesthetic depth of the subject based on the ratiocalculated by the temperature ratio calculating means.

In the above mentioned apparatus, the ratio of the peripheral bodytemperature measured by the peripheral body temperature measuring deviceto the deep body temperature measured by the deep body temperaturemeasuring device is calculated by the temperature ratio calculatingmeans. Then, based on the ratio calculated by the temperature ratiocalculating means, the anesthetic depth of the subject is determined bythe anesthetic depth determining means. Thus, the present apparatus canobjectively or quantitatively determine the anesthetic depth of thesubject. Additionally, the apparatus can accurately measure theanesthetic depth without needing operator's skill or the like.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic view for illustrating the construction of ananesthetic depth measuring apparatus embodying the present invention.

FIG. 2 is a block diagram for explaining various functions of a controldevice of the apparatus of FIG. 1.

FIG. 3 is a view for illustrating a fluctuation of pulse periods T_(RR)measured by the apparatus of FIG. 1.

FIG. 4 is a view for illustrating a first pulse period fluctuationsignal HFC_(RR), a second pulse period fluctuation signal LFC_(RR) and apulse period direct current component DC_(RR) which are extracted fromthe fluctuation of the pulse periods T_(RR) measured by the apparatus ofFIG. 1.

FIG. 5 is a graph showing a relationship used by the apparatus of FIG. 1for calculating an anesthetic depth D_(RR).

FIG. 6 is a graph showing a relationship used by the apparatus of FIG. 1for calculating an anesthetic depth D_(SYS).

FIG. 7 is a flow chart representing the operation of the control deviceof the apparatus of FIG. 1.

FIG. 8 is a block diagram corresponding to FIG. 2, for explainingvarious functions of a control device of an anesthetic depth measuringapparatus as another embodiment according to the present invention.

FIG. 9 is a graph showing a relationship between pulse periods T_(RR)and blood pressure values P_(SYS) of a non-anesthetized subject.

FIG. 10 is a graph showing a relationship between pulse periods T_(RR)and blood pressure values P_(SYS) of an anesthetized subject.

FIG. 11 is a graph showing a relationship used by the apparatus of FIG.8 for determining an anesthetic depth D based on a rate of changeΔT_(RR) /ΔP_(SYS).

FIG. 12 is a flow chart representing the operation of the control deviceof the apparatus of FIG. 8.

FIG. 13 is a diagrammatic view for illustrating the construction of ananesthetic depth measuring apparatus as yet another embodiment accordingto the present invention.

FIG. 14 is a block diagram for explaining various functions of a controldevice of the apparatus of FIG. 13.

FIG. 15 is a graph showing a relationship used by the apparatus of FIG.13 for determining an anesthetic depth D_(S) based on a temperaturedifference S (=T_(cent) -T_(dist)).

FIG. 16 is a graph showing a relationship used by the apparatus of FIG.13 for determining an anesthetic depth D_(R) based on a temperatureratio R (=T_(cent) /T_(dist)).

FIG. 17 is a flow chart representing the operation of the control deviceof the apparatus of FIG. 13.

THE BEST MODE FOR CARRYING OUT THE INVENTION

There will be described in detail an embodiment of the presentinvention, referring to the drawings.

FIG. 1 is a diagrammatic view for illustrating the construction of ananesthetic depth measuring apparatus embodying the present invention. Inthe figure, an electrocardiographic waveform detecting device 10includes a plurality of electrodes 12 which are put on a living subject.The device 10 continuously supplies a well-known electrocardiographicwaveform signal successively produced in synchronism with a heartbeat ofthe subject who is generally anesthetized by an inhalation anesthetic,such as isoflurane, to a CPU 18 of a control device 16 via an A/Dconverter 14.

A blood pressure measuring device 20 includes a pressure pulse wavedetecting probe 22 adapted to be pressed, with a band (not shown), to anartery of the subject, such as a carotid artery, a radial artery or apedal dorsal artery. The device 20 continuously measures a bloodpressure value of the generally anesthetized subject based on each onepulse of the detected pulse wave and supplies a blood pressure signalrepresentative of the blood pressure value to the CPU 18 of the controldevice 16 via an A/D converter 24. This blood pressure measuring device20 is constructed similarly to the blood pressure monitoring apparatusdisclosed in U.S. Pat. No. 4,423,738 or laid-open publication No.5-253196 of unexamined Japanese Patent Application.

The control device 16 is provided by a so-called microcomputer includingthe CPU 18, a ROM 26 and a RAM 28. The CPU 18 processes input signals,that is, the electrocardiographic waveform signal and the blood pressuresignal, according to control programs pre-stored in the ROM 26 byutilizing a temporary-storage function of the RAM 28, and controls adisplay device 30 so as to display an anesthetic depth D of the subject.

FIG. 2 is a block diagram for explaining various functions of thecontrol device 16. In the figure, a pulse period measuring means 50measures a pulse period from a heartbeat synchronous wave, such as anelectrocardiographic waveform, a pulse wave produced from an artery, orthe like, produced in synchronism with a heartbeat of the subject.Preferably, by calculating a time interval between each pair ofsuccessive two pulses of the electrocardiographic waveform, for example,R-waves of the successive two pulses, the pulse period measuring means50 continuously measures a pulse period T_(RR) of the anesthetizedsubject. The thus measured pulse periods T_(RR) have a fluctuation asshown in FIG. 3, for example.

A pulse period fluctuation signal extracting means 52 extracts, from thefluctuation of the pulse periods T_(RR) continuously measured by thepulse period measuring means 50, a first pulse period fluctuation signalHFC_(RR) which corresponds to a first pulse period fluctuation componentproduced in substantial synchronism with a respiration of the subjectand a second pulse period fluctuation signal LFC_(RR) which correspondsto a second pulse period fluctuation component having a predeterminedfrequency lower than a frequency of the first pulse period fluctuationcomponent. The pulse period fluctuation signal extracting means 52performs a frequency analysis of the fluctuation of the pulse periodsT_(RR), with a fast Fourier transformation (FFT) method, anautoregression (AR) method, or the like. Then, the pulse periodfluctuation signal extracting means 52 outputs, as the first and secondpulse period fluctuation signals HFC_(RR), LFC_(RR), a magnitude (power)of a signal component having a frequency in the neighborhood of thefrequency of the respiration of the subject and a magnitude (power) of asignal component having a frequency in the neighborhood of one third toone fourth of the frequency of the respiration of the subject,respectively. Specifically, the pulse period fluctuation signalextracting means 52 outputs, as the first and second pulse periodfluctuation signals HFC_(RR), LFC_(RR), a magnitude of a signalcomponent having a peak frequency in a predetermined frequency rangeincluding a frequency (e.g., 0.25 Hz) of the respiration of the subjectand a magnitude of a signal component having a peak frequency in apredetermined frequency range including a frequency (e.g., 0.07 Hz) ofabout one third to one fourth of the frequency of the respiration of thesubject, respectively. FIG. 4 respectively illustrates respectivemagnitudes of the first and second pulse period fluctuation signalsHFC_(RR), LFC_(RR) and a 0 Hz frequency component (direct currentcomponent) signal DC_(RR) which are extracted from the fluctuation ofthe pulse periods T_(RR).

A first anesthetic depth calculating means 54 included in an anestheticdepth determining means 62 calculates a first anesthetic depth D_(RR) ofthe subject based on a ratio (LFC_(RR) /HFC_(RR)) of the first pulseperiod fluctuation signal HFC_(RR) to the second pulse periodfluctuation signal LFC_(RR) which are extracted by the pulse periodfluctuation signal extracting means 52. The first anesthetic depthcalculating means 54 calculates the first anesthetic depth D_(RR) basedon the actual ratio (LFC_(RR) /HFC_(RR)) according to a pre-storedrelationship shown in FIG. 5, for example.

It is speculated that, in the action of a cardiac vagus nerve that is anefferent nerve originating from a circulatory center, a respiratoryfluctuation occurs due to the interference of a respiratory center withthe circulatory center at the level of a brain stem and a respiratoryfluctuation of afferent signals produced from cardio-pulmonaryreceptors. Therefore, a fluctuation appearing in a frequency of ignitionof a sino-auricular node can be regarded as a magnitude (power) of asignal component having a peak frequency in a frequency range includinga frequency (e.g., 0.25 Hz) of the respiration of the subject, that is,the first pulse period fluctuation signal HFC_(RR). Moreover, therespiratory fluctuation occurs to the action of a sympathetic nervewhich controls the sino-auricular node. However, since the pulse ratecontrol under the sympathetic nerve has a characteristic as a lowfrequency range filter, the sympathetic nerve can transmit only pulserate fluctuations having extremely low frequencies, e.g., frequenciesnot higher than 0.15 Hz, and HFC_(RR) having an ordinary respirationfrequency is exclusively mediated by the vagus nerve. Thus, theamplitude of HFC_(RR), that is, magnitude of HFC_(RR) is in proportionto the activity of the cardiac vagus nerve and may be used as a usefuland quantitative index of the cardiac vagus nerve activity. Meanwhile,it is speculated that the second pulse period fluctuation signalLFC_(RR) corresponding to a fluctuation component having a frequency ofabout one third to one fourth of a frequency of the first pulse periodfluctuation signal HFC_(RR) is caused by a pulse rate fluctuation whichoccurs via a baroreceptor reflex mechanism. Afferent and efferent nervesof the reflex are an aortic sinus nerve, and cardiac parasympathetic andsympathetic nerves, respectively. Since the signal LFC_(RR) is inproportion to a product of the amplitude of the blood pressure and thesensitivity of the baroreceptors, the sympathetic nerve activity cannotbe evaluated, if the baroreceptor reflex sensitivity is not constant.Thus, the ratio (LFC_(RR) /HFC_(RR)) closely corresponds to the nerveactivity, because of being freed from an influence of an individualdifference. The relationship shown in FIG. 5 is experimentally obtainedin advance, based on the above described facts.

A blood pressure measuring means 56 which is provided by, for example,the blood pressure measuring device 20, continuously measures a bloodpressure value of the subject. A blood pressure fluctuation signalextracting means 58 extracts, from a fluctuation of the blood pressurevalues, for example, systolic blood pressure values P_(SYS),continuously measured by the blood pressure measuring means 56, a bloodpressure fluctuation signal LFC_(SYS) which corresponds to a bloodpressure fluctuation component having a predetermined frequency lowerthan the frequency of the respiration of the subject. The blood pressurefluctuation signal extracting means 58 performs a frequency analysis ofthe fluctuation of the blood pressure values P_(SYS), with a fastFourier transformation (FFT) method, an autoregression (AR) method, orthe like, and outputs, as the blood pressure fluctuation signalLFC_(SYS), a magnitude (power) of a signal component having a peakfrequency in a frequency range including a frequency (e.g., 0.07 Hz) ofabout one third to one fourth of the frequency of the respiration of thesubject.

A second anesthetic depth calculating means 60 included in theanesthetic depth determining means 62 calculates a second anestheticdepth D_(SYS) of the subject based on a magnitude of the blood pressurefluctuation signal LFC_(SYS) according to a pre-stored relationship asshown in FIG. 6, for example. Since it is speculated that the bloodpressure fluctuation signal LFC_(SYS) representative of the fluctuationof blood pressure values results from a delay of a sympathetic vasomotorregulation system, an amplitude (magnitude) of the signal LFC_(SYS) maybe used as a quantitative index of a vasomotor sympathetic nerveactivity. A relationship shown in FIG. 6 is experimentally obtained inadvance, based on the above described facts.

The anesthetic depth determining means 62 determines a third anestheticdepth D based on the first anesthetic depth D_(RR) calculated by thefirst anesthetic depth calculating means 54 and the second anestheticdepth D_(SYS) calculated by the second anesthetic depth calculatingmeans 60. For example, if the first and second anesthetic depths D_(RR),D_(SYS) are extremely different from each other, the anesthetic depthdetermining means 62 judges, based on respective time-wise changes ofthe two anesthetic depths, which one of the two anesthetic depths D_(RR)and D_(SYS) is abnormal, and determines, as the third anesthetic depthD, the other of the anesthetic depths D_(RR) and D_(SYS), or calculatesrespective weighing factors based on the respective time-wise changes ofthe two anesthetic depths and determines, as the third anesthetic depthD, an average value of the respective weighed values of the anestheticdepths D_(RR) and D_(SYS). Meanwhile, if the first and second anestheticdepths D_(RR), D_(SYS) are not so different from each other, theanesthetic depth determining means 62 determines, as the thirdanesthetic depth D, one of the two anesthetic depths D_(RR), D_(SYS), oran average value of the two anesthetic depths D_(RR) and D_(SYS).

FIG. 7 is a flow chart representing the operation of the control device16, which shows a routine carried out in synchronism with a pulse or aninput of a blood pressure value.

In FIG. 7, at Step SA1 corresponding to the pulse period measuring means50, a pulse period T_(RR) is calculated as a time interval betweenrespective R-waves of successive two pulses of the electrocardiographicwaveform input from the electrocardiographic waveform detecting device10. Step SA1 is followed by Step SA2, corresponding to the pulse periodfluctuation signal extracting means 52, to perform a frequency analysisof a fluctuation of the pulse periods T_(RR) with a fast Fouriertransformation (FFT) method, an autoregression (AR) method, or the like,and extract, as first and second pulse period fluctuation signalsHFC_(RR), LFC_(RR), a magnitude (power) of a signal component having apeak frequency in a frequency range including a frequency (e.g., 0.25Hz) of a respiration of the subject and a magnitude (power) of a signalcomponent having a peak frequency in a frequency range including afrequency (e.g., 0.07 Hz) of about one third to one fourth of thefrequency of the respiration of the subject, respectively.

Step SA2 is followed by Step SA3, corresponding to the first anestheticcalculating means 54, to calculate a first anesthetic depth D_(RR) ofthe subject based on a ratio (LFC_(RR) /HFC_(RR)) of the first pulseperiod fluctuation signal HFC_(RR) to the second pulse periodfluctuation signal LFC_(RR) according to the pre-stored relationshipshown in FIG. 5, for example.

Next, the control of the CPU 18 goes to Step SA4. At Step SA4, a bloodpressure value P_(SYS) input from the blood pressure measuring device 20is read in. Step SA4 is followed by Step SA5, corresponding to the bloodpressure fluctuation signal extracting means 58, to perform a frequencyanalysis of a fluctuation of the blood pressure values P_(SYS), with afast Fourier transformation (FFT) method, an autoregression (AR) method,or the like, and extract, as the blood pressure fluctuation signalLFC_(SYS), a magnitude (power) of a signal component having a peakfrequency in a frequency range including a frequency (e.g., 0.07 Hz) ofabout one third to one fourth of the frequency of the respiration of thesubject.

Step SA5 is followed by Step SA6, corresponding to the second anestheticdepth calculating means 60, to calculate a second anesthetic depthD_(SYS) of the subject based on the blood pressure fluctuation signalLFC_(SYS) extracted at Step SA5 according to the pre-stored relationshipshown in FIG. 6, for example.

Subsequently, the control of the CPU 18 goes to Step SA7, correspondingto the anesthetic depth determining means 62, to determine a thirdanesthetic depth D having a higher reliability, based on the firstanesthetic depth D_(RR) calculated on the basis of the fluctuation ofpulse periods and the second anesthetic depth D_(SYS) calculated on thebasis of the fluctuation of blood pressure values. For example, if thefirst and second anesthetic depths D_(RR), D_(SYS) are extremelydifferent from each other, one of the first and second anesthetic depthsD_(RR), D_(SYS) is judged as an abnormal value, based on respectivetime-wise changes of the two anesthetic depths, and the other of thefirst and second anesthetic depths D_(RR), D_(SYS) is determined as thethird anesthetic depth D. If the first and second anesthetic depthsD_(RR), D_(SYS) are not so different from each other, an average valueof the first and second anesthetic depths D_(RR), D_(SYS) is determinedas the third anesthetic depth D. Step SA7 is followed by Step SA8 toquantitatively display, on the display device 30, the anesthetic depth Ddetermined at Step SA7, in digits, a trend graph, or the like. Forinstance, the anesthetic depth D is expressed with numerals by dividingthe axis of abscissas of FIG. 5 or 6 into predetermined units.

In the above described embodiment, from the fluctuation of the pulseperiods continuously measured at Step SA1 corresponding to the pulseperiod measuring means 50, the first pulse period fluctuation signalHFC_(RR) which corresponds to the first pulse period fluctuationcomponent produced in substantial synchronism with the respiration ofthe subject and the second pulse period fluctuation signal LFC_(RR)which corresponds to the second pulse period fluctuation componenthaving the predetermined frequency lower than the frequency of the firstpulse period fluctuation component are extracted at Step SA2corresponding to the pulse period fluctuation signal extracting means52. Then, the first anesthetic depth D_(RR) of the subject is calculatedat Step SA3 corresponding to the first anesthetic depth calculatingmeans 54, based on the ratio (LFC_(RR) /HFC_(RR)) of the first pulseperiod fluctuation signal HFC_(RR) to the second pulse periodfluctuation signal LFC_(RR). Thus, the present apparatus can objectivelyor quantitatively calculate the first anesthetic depth D_(RR) of thesubject and accurately obtain the anesthetic depth D_(RR) withoutneeding operator's skill or the like.

In the present embodiment, the blood pressure values P_(SYS) of thesubject are continuously measured by the blood pressure measuring means56. From the fluctuation of the continuously measured blood pressurevalues P_(SYS), the blood pressure fluctuation signal LFC_(SYS) whichcorresponds to the blood pressure fluctuation component having thepredetermined frequency lower than the frequency of the respiration ofthe subject is extracted at Step SA5 corresponding to the blood pressurefluctuation signal extracting means 58. Then, the second anestheticdepth D_(SYS) of the subject is calculated at Step SA6 corresponding tothe second anesthetic depth calculating means 60, based on the magnitudeof the blood pressure fluctuation signal LFC_(SYS). Thus, the presentapparatus can objectively or quantitatively calculate the secondanesthetic depth D_(SYS) of the subject and accurately obtain theanesthetic depth D_(SYS) without needing operator's skill or the like.

In the present embodiment, based on the first anesthetic depth D_(RR)calculated on the basis of the fluctuation of pulse periods T_(RR) andthe second anesthetic depth D_(SYS) on the basis of the fluctuation ofblood pressure values P_(SYS), the third anesthetic depth D having ahigher reliability is determined at Step SA7 corresponding to theanesthetic depth determining means 62, whereby the anesthetic depth Dquantitatively displayed on the display device 30 enjoys the higherreliability.

Next, there will be described another embodiment according to thepresent invention. Hereinafter, the same parts as those of the priorembodiment are denoted by the same reference numerals and the detaildescription thereof is omitted.

FIG. 8 is a block diagram for explaining various functions of thecontrol device 16 of an anesthetic depth measuring apparatus as anotherembodiment according to the present invention. In the figure, a changerate calculating means 64 calculates a rate of change, ΔT_(RR)/ΔP_(SYS), of a pulse period T_(RR) to a blood pressure value P_(SYS),based on the blood pressure values, for example, systolic blood pressurevalues P_(SYS) continuously measured by the blood pressure measuringmeans 56 and the pulse periods T_(RR) measured by the pulse periodmeasuring means 50, within a predetermined unit time which correspondsto, for example, ten pulses to several tens of pulses. For example, therate of change ΔT_(RR) /ΔP_(SYS) is calculated as a slope or inclinationof a regression line determined on data points indicating actual bloodpressure values P_(SYS) and actual pulse periods T_(RR) of the subjectin a two-dimensional coordinate system defined by a first axisindicative of blood pressure values P_(SYS) and a second axis indicativeof pulse periods T_(RR).

When each data point indicative of an actual blood pressure valueP_(SYS) and an actual pulse period T_(RR) of the anesthetized subject isplotted in the two-dimensional coordinate system defined by the firstaxis indicative of blood pressure values P_(SYS) and the second axisindicative of pulse periods T_(RR), eventually those data points arelocated along a straight line. Thus, the blood pressure values and thepulse periods are related to each other. The rate of change ΔT_(RR)/ΔP_(SYS) indicates the inclination of the straight line. When thesubject is not anesthetized, the inclination of the straight lineindicates a large value as shown in FIG. 9, for example. When thesubject is anesthetized, the inclination of the straight line indicatesa small value as shown in FIG. 10, for example. As one of nerve-basedcirculation control mechanisms, there is known a baroreceptor reflexwhich acts via an automatic nerve. The baroreceptor reflex causes aneffector organ such as the heart, peripheral blood vessels, or the liketo adjust heart rate or arterial pressure so as to eliminate changes ofthe blood pressure and keep the blood pressure constant. Further, thebaroreceptor reflex not only reacts to changes of blood vessels due to aphysiological stress, a postural change or a bleeding, but also isinfluenced by an anesthetic agent. Therefore, the rate of change ΔT_(RR)/ΔP_(SYS) changes according to the anesthetic depth. A relationshipshown in FIG. 11 is experimentally obtained in advance, based on theabove described facts.

An anesthetic depth determining means 66 determines an anesthetic depthD of the subject based on the rate of change ΔT_(RR) /ΔP_(SYS)calculated by the change rate calculating means 64 according to thepre-stored relationship shown in FIG. 11.

FIG. 12 is a flow chart representing the operation of the control device16 of the second apparatus, which shows a routine carried out insynchronism with a pulse or an input of a blood pressure value, or at apredetermined regular time interval or a predetermined unit of pulses.

In FIG. 12, at Step SB1 corresponding to the pulse period measuringmeans 50, a pulse period T_(RR) is calculated as a time interval betweenrespective R-waves of successive two pulses of the electrocardiographicwaveform input from the electrocardiographic waveform detecting device10. Step SB1 is followed by Step SB2 to read in, for example, a systolicblood pressure value P_(SYS) measured by the blood pressure measuringdevice 20 corresponding to the blood pressure measuring means 56.

Step SB2 is followed by Step SB3, corresponding to the change ratecalculating means 64, to calculate a rate of change ΔT_(RR) /ΔP_(SYS) asan inclination of a regression line obtained from a plurality of datapoints each indicating an actual blood pressure value P_(SYS) and anactual pulse period T_(RR) of the subject that are plotted in atwo-dimensional coordinate system defined by a first axis indicative ofblood pressure values P_(SYS) and a second axis indicative of pulseperiods T_(RR).

Subsequently, the control of the CPU 18 goes to Step SB4, correspondingto the anesthetic depth determining means 66, to determine an anestheticdepth D of the subject based on the rate of change ΔT_(RR) /ΔP_(SYS)calculated at Step SB3 according to the pre-stored relationship shown inFIG. 11, for example. Step SB4 is followed by Step SB5 to display, onthe display device 30, the determined anesthetic depth D in digits, atrend graph, or the like.

In the above mentioned embodiment, the rate of change ΔT_(RR) /ΔP_(SYS)is calculated at Step SB3 corresponding to the change rate calculatingmeans 64, based on the pulse periods T_(RR) continuously measured atStep SB1 corresponding to the pulse period measuring means 50 and theblood pressure values P_(SYS) continuously measured by the bloodpressure measuring means 56. Then, the anesthetic depth D is determinedat Step SB4 corresponding to the anesthetic depth determining means 66,based on the rate of change ΔT_(RR) /ΔP_(SYS) according to therelationship shown in FIG. 11. Thus, the second apparatus canobjectively and quantitatively determine the anesthetic depth D of thesubject and accurately obtain the anesthetic depth D without needingoperator's skill or the like.

FIG. 13 is a diagrammatic view for illustrating the construction of ananesthetic depth measuring apparatus as yet another embodiment accordingto the present invention. In the figure, a peripheral body temperaturemeasuring device 110 includes a peripheral body temperature measuringprobe 112 which is worn on a living subject. The peripheral bodytemperature measuring device 110 measures a peripheral body temperatureof the subject who is generally anesthetized by an inhalationanesthetic, such as isoflurane, and successively supplies a peripheralbody temperature signal representative of the measured peripheral bodytemperature to a CPU 118 of a control device 116 via an A/D converter114. The peripheral body temperature measuring probe 112 includes athermistor, for example, and is adhered to a skin of the subject, suchas a forehead or a sole.

A deep body temperature measuring device 120 includes a deep bodytemperature measuring probe 122 which is worn on the subject. The deepbody temperature measuring device 120 measures a deep body temperature,that is, a central body temperature of the generally anesthetizedsubject, and successively supplies a deep body temperature signalrepresentative of the measured deep body temperature to the CPU 118 viaan A/D converter 124. The deep body temperature measuring probe 122 isconstructed such that a temperature sensor portion thereof is insulatedby a thermal insulator so that the sensor portion is brought intoequilibrium with the deep body temperature of the subject. Otherwise,the deep body temperature measuring probe 122 may be provided by aninsertion-type probe which is inserted into a rectum or an esophagus andmeasures a deep body temperature of a living the subject.

The control device 116 is provided by a so-called microcomputerincluding the CPU 118, a ROM 126 and a RAM 128. The CPU 118 processesinput signals, that is, the peripheral body temperature signal and thedeep body temperature signal, according to control programs pre-storedin the ROM 126 by utilizing a temporary-storage function of the RAM 128,and controls a display device 130 to display an anesthetic depth D ofthe subject.

FIG. 14 is a block diagram for explaining various functions of thecontrol device 116. In the figure, a peripheral body temperaturemeasuring means 150 corresponds to the peripheral body temperaturemeasuring device 110 and measures a peripheral body temperature on abody surface of the subject. A deep body temperature measuring means 152corresponds to the deep body temperature measuring device 120 andmeasures a deep body temperature in a central (deep) portion of thesubject.

A temperature difference calculating means 154 calculates a difference S(=T_(cent) -T_(dist)) between the peripheral body temperature T_(dist)measured by the peripheral body temperature measuring means 150 and thedeep body temperature T_(cent) measured by the deep body temperaturemeasuring means 152. An anesthetic depth determining means 156determines an anesthetic depth D_(S) based on the actual difference Saccording to a pre-stored relationship shown in FIG. 15, for example.

Meanwhile, a temperature ratio calculating means 158 calculates a ratioR (T_(cent) /T_(dist)) of the peripheral body temperature T_(dist)measured by the peripheral body temperature measuring means 150 to thedeep body temperature T_(cent) measured by the deep body temperaturemeasuring means 152. The anesthetic depth determining means 156determines an anesthetic depth D_(R) based on the actual ratio Raccording to a pre-stored relationship shown in FIG. 16, for example.Further, the anesthetic depth determining means 156 determines a morereliable anesthetic depth D from the anesthetic depth D_(S) determinedbased on the difference S and the anesthetic depth D_(R) determinedbased on the ratio R.

Generally, blood vessels of an anesthetized patient tend to be relaxedand dilated. In this case, blood circulation of subject's peripheralportion is promoted and the peripheral body temperature T_(dist) israised. Therefore, as the difference S (=T_(cent) -T_(dist)) between theperipheral body temperature T_(dist) and the deep body temperature(central temperature) T_(cent) or the ratio R (=T_(cent) /T_(dist)) ofthe central body temperature T_(cent) to the peripheral body temperatureT_(dist) decreases, an anesthetic effect increases and the anestheticdepth D increases. The relationships shown in FIGS. 15 and 16 areexperimentally obtained in advance, based on the above described facts.

FIG. 17 is a flow chart representing the operation of the control device116, which shows a routine carried out in synchronism with an input of aperipheral or a deep body temperature T_(dist), T_(cent).

In FIG. 17, at Step SC1, a peripheral body temperature T_(dist) measuredby the peripheral body temperature measuring device 110 is read in. StepSC1 is followed by Step SC2 to read in a deep body temperature T_(cent)measured by the deep body temperature measuring device 120. Step SC2 isfollowed by Step SC3, corresponding to the temperature differencecalculating means 154, to calculate a difference S (=T_(cent) -T_(dist))between the deep body temperature T_(cent) and the peripheral bodytemperature T_(dist). Step SC3 is followed by Step SC4, corresponding tothe anesthetic depth determining means 156, to determine an anestheticdepth D_(S) based on the actual difference S (=T_(cent) -T_(dist))according to the pre-stored relationship shown in FIG. 15.

Subsequently, the control of the CPU 118 goes to Step SC5, correspondingto the temperature ratio calculating means 158. At Step SC5, a ratio R(=T_(cent) /T_(dist)) of the central body temperature T_(cent) to theperipheral body temperature T_(dist) is calculated. Step SC5 is followedby Step SC6, corresponding to the anesthetic depth determining means156, to determine an anesthetic depth D_(R) based on the actual ratio R(=T_(cent) /T_(dist)) according to the pre-stored relationship shown inFIG. 16.

Step SC6 is followed by Step SC7, corresponding to the anesthetic depthdetermining means 156, to determine a more reliable anesthetic depth Dbased on the anesthetic depths D_(S) and D_(R) determined on the basisof the difference S (=T_(cent) -T_(dist)) and the ratio R (=T_(cent)/T_(dist)), respectively. For example, if the two anesthetic depthsD_(S) and D_(R) are extremely different from each other, one of the twoanesthetic depths is judged as an abnormal value, based on respectivetime-wise changes of the two anesthetic depth, and the other of the twoanesthetic depths is determined as the anesthetic depth D. If the twoanesthetic depths D_(S) and D_(R) are not so different from each other,an average value of the two anesthetic depths is determined as theanesthetic depth D.

Step SC7 is followed by Step SC8 to quantitatively display, on thedisplay device 130, the anesthetic depth D determined at Step SC7 indigits, a trend graph, or the like. For instance, the anesthetic depth Dis expressed with numerals by dividing the axis of abscissas of FIG. 15or 16 into predetermined units.

In the above mentioned embodiment, at Step SC3 corresponding to thetemperature difference calculating means 154, the difference S(=T_(cent) -T_(dist)) between the deep body temperature T_(cent)measured by the deep body temperature measuring means 152 and theperipheral body temperature T_(dist) measured by the peripheral bodytemperature measuring means 150 is calculated. At Step SC4 correspondingto the anesthetic depth determining means 156, the anesthetic depthD_(S) of the subject is determined on the basis of the difference S(=T_(cent) -T_(dist)). Thus, the present apparatus can to objectively orquantitatively determine the anesthetic depth D_(S) of the subject andaccurately obtain the anesthetic depth D_(S) without needing operator'sskill or the like.

Further, in the present embodiment, at Step SC5 corresponding to thetemperature ratio calculating means 158, the ratio R (=T_(cent)/T_(dist)) of the central body temperature T_(cent) measured by the deepbody temperature measuring means 152 to the peripheral body temperatureT_(dist) measured by the peripheral body temperature measuring means 150is calculated. At Step SC6 corresponding to the anesthetic depthdetermining means 156, the anesthetic depth D_(R) of the subject isdetermined on the basis of the ratio R (=T_(cent) /T_(dist)) calculatedby the temperature ratio calculating means 158. Thus, the presentapparatus can objectively or quantitatively determine the anestheticdepth D_(S) of the subject and accurately obtain the anesthetic depthD_(S) without needing operator's skill or the like.

In the present embodiment, at Step SC7 corresponding to the anestheticdepth determining means 156, the anesthetic depth D having a higherreliability is determined, based on the anesthetic depth D_(S)determined on the basis of the temperature difference S (=T_(cent)-T_(dist)) and the anesthetic depth D_(R) determined on the basis of thetemperature ratio R (=T_(cent) /T_(dist)), whereby the anesthetic depthD quantitatively displayed on the display device 130 enjoys the highreliability.

While the present invention has been described in its preferredembodiments by reference to the drawings, it is to be understood thatthe invention may otherwise be embodied.

In the embodiment shown in FIG. 2, both the means 50, 52, 54 forcalculating the first anesthetic depth D_(RR) from the fluctuation ofthe pulse periods T_(RR), and the means 56, 58, 60 for calculating thesecond anesthetic depth D_(SYS) from the fluctuation of the bloodpressure values P_(SYS) are employed. However, even if one of the twomeans for calculating the first and second anesthetic depths D_(RR),D_(SYS) is omitted, the apparatus can have the function of measuring ananesthetic depth.

Moreover, in the embodiment of FIG. 2, the pulse period T_(RR) of thesubject is continuously measured by calculating a period of anelectrocardiographic waveform (ECG) detected by the electrocardiographicwaveform detecting device 10, for example, calculating a time intervalbetween respective R-waves of each pair of successive two pulses of theelectrocardiographic waveform. However, it is possible to employ a meansfor pulse-synchronously calculating a period of a pulse wave detected bya well-known cuff or pressure pulse wave sensor from an artery of aliving subject, or a means for pulse-synchronously calculating a periodof a volume pulse wave detected by a photoelectric pulse wave sensor. Inshort, any kind of means for continuously measuring a pulse period ofthe subject may be provided. For example, when a pulse period ismeasured on the basis of the pressure pulse wave detected by thepressure pulse wave detecting probe 22 of the blood pressure measuringdevice 20, the electrocardiographic detecting device 10 is not needed.

In the embodiment shown in FIG. 2, as the pulse period T_(RR), the bloodpressure value P_(SYS), or the anesthetic depth D_(RR) or D_(SYS), amoving average of values pulse-synchronously obtained within apredetermined period may be used. Further, the pulse period T_(RR) orthe blood pressure value P_(SYS) may be obtained based on every secondor third pulse.

In the embodiment shown in FIG. 2, the pulse period fluctuation signalextracting means 52 or the blood pressure fluctuation signal extractingmeans 58 may be provided by a digital filter for discriminating amicro-oscillation signal having a low frequency.

In the embodiment shown in FIG. 2, for the anesthetic depth D_(SYS)calculation, the fluctuation of the systolic blood pressure valuesP_(SYS) measured by the blood pressure measuring means 56 are used.However, a fluctuation of mean blood pressure values P_(MEAN) ordiastolic blood pressure values P_(DIA) measured by the blood pressuremeasuring means 56 may be used.

In the embodiment shown in FIG. 2, the first and second pulse periodfluctuation signals HFC_(RR), LFC_(RR) are obtained from the pulseperiods T_(RR) continuously measured by the pulse period measuring means50. However, since the pulse period T_(RR) (sec.) corresponds to a pulserate PR (=60/T_(RR)), one to one, a means for measuring a pulse rate PRmay be employed in place of the pulse period measuring means 50, and,from a fluctuation of the pulse rates PR, a first pulse rate fluctuationsignal corresponding to a respiratory fluctuation and a second pulserate fluctuation signal corresponding to one third to one fourth of therespiratory fluctuation may obtained.

In the embodiment shown in FIG. 2, the first anesthetic depth D_(RR) ofthe subject is calculated on the basis of the ratio (LFC_(RR) /HFC_(RR))of the second pulse period fluctuation signal LFC_(RR) to the firstpulse period fluctuation signal HFC_(RR) and the second anesthetic depthD_(SYS) is calculated on the basis of the magnitude of the bloodpressure fluctuation signal LFC_(SYS). However, the ratio (LFC_(RR)/HFC_(RR)) or the blood pressure fluctuation signal LFC_(SYS) may becorrected or modified based on other parameters. In any case, the firstanesthetic depth D_(RR) of the subject is calculated on the basis of theratio (LFC_(RR) /HFC_(RR)) of the second pulse period fluctuation signalLFC_(RR) to the first pulse period fluctuation signal HFC_(RR) and thesecond anesthetic depth D_(SYS) is calculated on the basis of themagnitude of the blood pressure fluctuation signal LFC_(SYS).

In the embodiment shown in FIG. 8, the rate of change ΔT_(RR) /ΔP_(SYS)of the pulse period T_(RR) to the blood pressure value P_(SYS) iscalculated and the anesthetic depth D is calculated on the basis of therate of change ΔT_(RR) /ΔP_(SYS). However, a rate of change ΔP_(SYS)/ΔT_(RR) of the blood pressure value P_(SYS) to the pulse period T_(RR)may be used. The rate of change ΔP_(SYS) /ΔT_(RR) increases withincreasing of the anesthetic depth D.

In the embodiment shown in FIG. 8, the pulse period T_(RR) is used.However, a heart rate HR may be used. Since the pulse period T_(RR) isthe inverse of the heart rate HR, a rate of change of the heart rate HRto the blood pressure value P_(SYS) can be regarded as substantially thesame as the rate of change ΔT_(RR) /ΔP_(SYS).

In the embodiment shown in FIG. 8, the pulse period T_(RR) and the bloodpressure value P_(SYS) are measured corresponding to each one pulse.However, the pulse period T_(RR) and the blood pressure value P_(SYS)may be measured at a predetermined regular interval which corresponds totwo or more pulses. In addition, the pulse period T_(RR) and the bloodpressure value P_(SYS) may be measured during an operation period whichis started and ended at a predetermined cycle.

In the embodiment shown in FIG. 8, the pulse period T_(RR) of thesubject is continuously measured by calculating a period of anelectrocardiographic waveform (ECG) detected by the electrocardiographicwaveform detecting device 10, for example, calculating a time intervalbetween respective R-waves of each pair of successive two pulses of theelectrocardiographic waveform. However, it is possible to employ a meansfor pulse-synchronously calculating a period of a pulse wave detected bya well-known cuff or pressure pulse wave sensor from an artery of aliving subject, or a means for pulse-synchronously calculating a periodof a volume pulse wave detected by a photoelectric pulse wave sensor. Inshort, any kind of means for continuously measuring a pulse period ofthe subject may be provided. For example, when a pulse period ismeasured on the basis of the pressure pulse wave detected by thepressure pulse wave detecting probe 22 of the blood pressure measuringdevice 20, the electrocardiographic detecting device 10 is not needed.

In the embodiment shown in FIG. 8, the systolic blood pressure valuesP_(SYS) measured by the blood pressure measuring device 20 are used.However, the mean blood pressure values P_(MEAN) or the diastolic bloodpressure values P_(DIA) may be used.

In the embodiment shown in FIG. 8, as the pulse period T_(RR) or theblood pressure value P_(SYS), a moving average of valuespulse-synchronously obtained within a predetermined duration may beused.

In the embodiment shown in FIG. 8, the anesthetic depth D is determinedon the basis of the rate of change ΔT_(RR) /ΔP_(SYS). However, the rateof change ΔT_(RR) /ΔP_(SYS) may be corrected or modified based on otherparameters. In any case, the anesthetic depth D is determined on thebasis of the rate of change ΔT_(RR) /ΔP_(SYS).

In the embodiment shown in FIG. 13, both the means 154 and Steps SC3 andSC4 for calculating the anesthetic depth D_(S) based on the temperaturedifference S (=T_(cent) -T_(dist)), and the means 158 and Steps SC5 andSC6 for calculating the anesthetic depth D_(R) based on the temperatureratio R (=T_(cent) /T_(dist)) are employed. However, one of theabove-indicated two anesthetic depth determining devices may be omitted.

In the embodiment shown in FIG. 13, the anesthetic depths D_(S) andD_(R) are calculated on the basis of the temperature difference S(=T_(cent) -T_(dist)) and the temperature ratio R (=T_(cent) /T_(dist)),respectively. However, the temperature difference S (=T_(cent)-T_(dist)) or the temperature ratio R (=T_(cent) /T_(dist)) may becorrected or modified based on other parameters. In any case, theanesthetic depth D_(S) or D_(R) is calculated on the basis of thetemperature difference S (=T_(cent) -T_(dist)) or the temperature ratioR (=T_(cent) /T_(dist)), respectively.

It is to be understood that the present invention may be embodied withother changes and modifications that may occur to those skilled in theart without departing from the scope of the invention.

INDUSTRIAL UTILITY

It is understood from the above description that since the anestheticdepth measuring apparatuses according to the present invention canquantitatively and objectively measure an anesthetic depth of a patient,they are suitable for use in an operating room, an intensive care unit,or the like where the patient is generally anesthetized.

We claim:
 1. An anesthetic depth measuring apparatus for measuring ananesthetic depth of a living subject, characterized by comprising:apulse period measuring device which continuously measures a period of apulse of the subject; pulse period fluctuation signal extracting meansfor extracting, from a fluctuation of the pulse periods continuouslymeasured by said pulse period measuring device, a first pulse periodfluctuation signal which corresponds to a first pulse period fluctuationcomponent produced in substantial synchronism with a respiration of thesubject and a second pulse period fluctuation signal which correspondsto a second pulse period fluctuation component having a predeterminedfrequency lower than a frequency of the first pulse period fluctuationcomponent; and anesthetic depth calculating means for calculating ananesthetic depth of the subject based on a ratio of said first pulseperiod fluctuation signal to said second pulse period fluctuationsignal.
 2. An anesthetic depth measuring apparatus according to claim 1,wherein said pulse period fluctuation signal extracting means extracts,as said first pulse period fluctuation signal, pulse period fluctuationcomponents having frequencies in a predetermined frequency rangeincluding a frequency of the respiration of the subject.
 3. Ananesthetic depth measuring apparatus according to claim 1, wherein saidpulse period fluctuation signal extracting means extracts, as saidsecond pulse period fluctuation signal, pulse period fluctuationcomponents having frequencies in a predetermined frequency rangeincluding a frequency of about one third to one fourth of a frequency ofthe respiration of the subject.
 4. An anesthetic depth measuringapparatus for measuring an anesthetic depth of a living subject,characterized by comprising:a pulse period measuring device whichcontinuously measures a period of a pulse of the subject; pulse periodfluctuation signal extracting means for extracting, from a fluctuationof the pulse periods continuously measured by said pulse periodmeasuring device, a first pulse period fluctuation signal whichcorresponds to a first pulse period fluctuation component produced insubstantial synchronism with a respiration of the subject and a secondpulse period fluctuation signal which corresponds to a second pulseperiod fluctuation component having a predetermined frequency lower thana frequency of the first pulse period fluctuation component; firstanesthetic depth calculating means for calculating a first anestheticdepth of the subject based on a ratio of said first pulse periodfluctuation signal to said second pulse period fluctuation signal; ablood pressure measuring device which continuously measures a bloodpressure value of the subject; blood pressure fluctuation signalextracting means for extracting, from a fluctuation of the bloodpressure values continuously measured by said blood pressure measuringdevice, a blood pressure fluctuation signal which corresponds to a bloodpressure fluctuation component having a predetermined frequency lowerthan a frequency of a respiration of the subject; second anestheticdepth calculating means for calculating a second anesthetic depth of thesubject based on a magnitude of said blood pressure fluctuation signal;and anesthetic depth determining means for determining a thirdanesthetic depth of the subject based on the first anesthetic depthcalculated by said first anesthetic depth calculating means and thesecond anesthetic depth calculated by said second anesthetic depthcalculating means, so that the determined third anesthetic depth isdisplayed on a display device.